Re: [PATCH 0/6] rcu: Remove several redundant memory barriers

Valentin Schneider
2024-05-15T17:32:46Z

On 15/05/24 14:53, Frederic Weisbecker wrote:
> Reviewing Valentin's patchset made me stare at some memory barriers
> on the way.

Sorry not sorry? :-)

> Here is some removal proposal. Some may be beneficial on
> runtime (fqs snapshot with potentially as many smp_mb() as the number
> of online CPUs for each GP). Some happen on more rare path. In any
> case they clarify code reviews so we don't stumble upon mysterious
> barriers.
>
> Thanks.
>
> Frederic Weisbecker (6):
> rcu: Remove full ordering on second EQS snapshot
> rcu: Remove superfluous full memory barrier upon first EQS snapshot
> rcu/exp: Remove superfluous full memory barrier upon first EQS
> snapshot
> rcu: Remove full memory barrier on boot time eqs sanity check
> rcu: Remove full memory barrier on RCU stall printout
> rcu/exp: Remove redundant full memory barrier at the end of GP
>
> .../Tree-RCU-Memory-Ordering.rst | 6 +++---
> kernel/rcu/tree.c | 21 +++++++------------
> kernel/rcu/tree_exp.h | 16 +++++++++++---
> kernel/rcu/tree_stall.h | 4 ++--
> 4 files changed, 26 insertions(+), 21 deletions(-)
>
> --
> 2.44.0